Showcase cooling device

ABSTRACT

There is disclosed a showcase cooling device which is capable of cooling all of a plurality of showcases with no difficulty, while suppressing a power consumption of a compressor. A showcase cooling device  1  distributes and supplies a refrigerant discharged from a compressor to evaporators disposed in a plurality of showcases  3 A to  3 H, and comprises chamber inside temperature sensors which detect chamber inside temperatures of the showcases  3 A to  3 H, respectively, and control means for controlling an operation of the compressor, and this control means controls the operation of the compressor on the basis of the chamber inside temperature of the showcase that is hardest to cool among the respective showcases  3 A to  3 H.

TECHNICAL FIELD

The present invention relates to a showcase cooling device in which arefrigerant discharged from a compressor is distributed and supplied toevaporators of a plurality of showcases and each of the showcases iscooled.

BACKGROUND ART

Heretofore, a plurality of showcases have been installed in an interiorof a store such as a convenience store, and a refrigerant has beendistributed and supplied to evaporators of the respective showcases froma compressor of a refrigerating machine installed in an exterior of thestore, or the like. In this case, the refrigerant compressed in thecompressor radiates heat in a condenser similarly disposed in therefrigerating machine, and is condensed and then supplied to each of theshowcases through a refrigerant pipe constituting a refrigerant circuit.In the showcase, an expansion valve and the evaporator are disposed, andthe refrigerant is throttled in the expansion valve and then flows intothe evaporator in which the refrigerant evaporates, thereby cooling coldair to be circulated in a chamber of the showcase (e.g., see PatentDocument 1).

In addition, a throttle degree of the expansion valve is regulated sothat a superheat degree of the refrigerant flowing out from theevaporator has the most suitably predetermined value, and realizesefficient cooling of the showcase and prevention of liquid back to thecompressor, but as this expansion valve, a mechanical type and anelectronic type (an electric expansion valve) are present. In the caseof the mechanical expansion valve, the valve self-sustainably operatesto obtain the predetermined superheat degree set to itself (thepredetermined value), and in the case of the electronic expansion valve,a valve open degree is controlled by a control device so that a targetsuperheat degree is obtained. Additionally, in a previous stage of eachexpansion valve, a liquid solenoid valve is disposed, and in a statewhere an inside of the chamber of the showcase is sufficiently cooled,this liquid solenoid valve is closed (in the case of the electronicexpansion valve, the valve itself can fully be closed, and hence, theliquid solenoid valve is not disposed in a certain case).

In addition, for example, an operation frequency of the compressor isusually controlled on the basis of a low pressure of the refrigerantcircuit. In this case, a target low pressure is set to such a value thateach of the showcases can sufficiently be cooled, on the basis of, e.g.,enthalpy in the store by the control device, and the operation frequencyof the compressor is controlled so that the low pressure becomes thistarget low pressure. It is to be noted that such ability control of thecompressor is not limited to the operation frequency, and a plurality ofcompressors are disposed to change the number of the compressors to beoperated in a certain case.

CITATION LIST Patent Documents

Patent Document 1: Publication of Japanese Patent No. 5053527

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Here, loads (ambient temperature or humidity, influence of wind, chamberinside temperature control or defrosting control to cool commodities ondisplay, etc.) in a plurality of showcases vary, respectively, andhence, opening/closing of a liquid solenoid valve (a valve open degreein the case of an electronic expansion valve) depends on these loads. Onthe other hand, heretofore, an operation frequency of a compressor hasbeen controlled on the basis of a low pressure of a refrigerant circuit,and hence, in a situation where the opening/closing of liquid solenoidvalves of the plurality of showcases is simultaneously or substantiallysimultaneously performed (i.e., a situation where the opening/closing issynchronously performed) or in a situation where, in the case of theelectronic expansion valve, regulating directions of valve open degreeshave the same tendency in the plurality of electronic expansion valves(the same tendency is a tendency that the valves close at the same time,and the valves fully close in the most remarkable case, or the sametendency is a tendency that the valves open at the same time, and thevalves fully open in the most remarkably case) and regulation issimultaneously or substantially simultaneously performed, a fluctuationof the low pressure enlarges, and due to an influence of thefluctuation, the operation frequency of the compressor also fluctuates.That is, when the cooling load fluctuates due to the opening and closingof the liquid solenoid valve of the showcase, the low pressurefluctuates, and hence, ease of cooling in the other showcases changes,so that operations are chained. Further, the operation frequency of thecompressor noticeably fluctuates to inhibit this low pressurefluctuation.

In consequence, heretofore, the operation frequency of the compressorhas excessively been concerned with the low pressure and thereforenoticeably fluctuated, with the result that a power consumption hasincreased. In addition, as described above, the load varies with therespective showcases, whereas the target low pressure is set to such avalue that all the showcases can sufficiently been cooled, which causesa situation where the ability of the compressor is excessive for theshowcase that is easy to cool (e.g., the showcase on which the load islight) and also causes an energy loss.

The present invention has been developed to solve such a conventionaltechnical problem, and an object thereof is to provide a showcasecooling device which is capable of cooling all showcases with nodifficulty, while suppressing a power consumption of a compressor.

Means for Solving the Problems

To solve the above problems, a showcase cooling device of the presentinvention distributes and supplies a refrigerant discharged from acompressor to evaporators disposed in a plurality of showcases,comprises chamber inside temperature sensors which detect chamber insidetemperatures of the showcases, respectively, and control means forcontrolling an operation of the compressor, and is characterized in thatthis control means controls the operation of the compressor on the basisof the chamber inside temperature of the showcase that is hardest tocool among the respective showcases.

The showcase cooling device of the invention of claim 2 is characterizedin that, in the above invention, each of the showcases comprisessuperheat degree regulating means for throttling the refrigerant flowinginto the evaporator and regulating, into a predetermined value, thesuperheat degree of the refrigerant flowing out from the evaporator, andan opening/closing valve which controls the inflow of the refrigerantinto the evaporator, and the control means controls the operation of thecompressor on the basis of the chamber inside temperature of theshowcase that is hardest to cool, sets a target superheat degree of theother showcase on the basis of the chamber inside temperatures of theother showcases, and opens and closes the opening/closing valve of theother showcases on the basis of this target superheat degree and thepredetermined value of the superheat degree.

The showcase cooling device of the invention of claim 3 is characterizedin that, in the invention of claim 1, each of the showcases comprisessuperheat degree regulating means for throttling the refrigerant flowinginto the evaporator and regulating, into a predetermined value, thesuperheat degree of the refrigerant flowing out from the evaporator, andan opening/closing valve which controls the inflow of the refrigerantinto the evaporator, and the control means controls the operation of thecompressor on the basis of the chamber inside temperature of theshowcase that is hardest to cool, opens and closes the opening/closingvalve of the other showcases on the basis of the chamber insidetemperatures of the other showcases, and executes the opening andclosing of the respective opening/closing valves at different timings,when the opening/closing valves of the other showcases of the othershowcases are opened and closed.

The showcase cooling device of the invention of claim 4 is characterizedin that, in the invention of claim 1, each of the showcases comprises anexpansion valve which throttles the refrigerant flowing into theevaporator and controls, into a target superheat degree, the superheatdegree of the refrigerant flowing out from the evaporator, and thecontrol means defines, as a predetermined value, the target superheatdegree of the showcase that is hardest to cool to control a valve opendegree of an expansion valve of the showcase, controls the operation ofthe compressor on the basis of the chamber inside temperature of theshowcase, sets the target superheat degree of the other showcases on thebasis of the chamber inside temperatures of the other showcases, andcontrols the valve open degree of the expansion valve of the othershowcases.

The showcase cooling device of the invention of claim 5 is characterizedin that, in the above respective inventions, the control meansdistinguishes the showcase that is hardest to cool among the respectiveshowcases, and in a case where there is present the other showcase thatis harder to cool than the showcase in which the operation of thecompressor is controlled on the basis of the chamber inside temperature,the control means switches to a state to control the operation of thecompressor on the basis of the chamber inside temperature of the othershowcase.

The showcase cooling device of the invention of claim 6 is characterizedin that, in the above invention, the control means distinguishes theshowcase that is hardest to cool among the respective showcases, in astate where the chamber inside temperature is stabilized.

The showcase cooling device of the invention of claim 7 is characterizedin that, in the above respective inventions, the control means controlsan operation frequency of the compressor on the basis of the chamberinside temperature of the showcase that is hardest to cool.

The showcase cooling device of the invention of claim 8 is characterizedin that the above invention comprises a blowout temperature sensordisposed in a cold air blowout portion of each of the showcases todetect a blowout temperature of the cold air to each of the showcases,and the control means determines a target blowout temperature of thecold air to the showcase by a PID calculation based on a deviationbetween the chamber inside temperature of the showcase and a set valueof the chamber inside temperature, and determines a target operationfrequency of the compressor and/or the target superheat degree by a PIDcalculation based on a deviation between the blowout temperaturedetected by the blowout temperature sensor and the target blowouttemperature.

The showcase cooling device of the invention of claim 9 is characterizedin that the invention of claim 7 comprises evaporator temperaturesensors to detect temperatures of the evaporators of the showcases,respectively, and the control means determines a target evaporatortemperature of each of the showcases by a PID calculation based on adeviation between the chamber inside temperature of the showcase and aset value of the chamber inside temperature, and determines a targetoperation frequency of the compressor and/or the target superheat degreeby a PID calculation based on a deviation between the temperature ofeach of the evaporators which is detected by the evaporator sensor andthe target evaporator temperature.

Advantageous Effect of the Invention

According to the present invention, a showcase cooling device, whichdistributes and supplies a refrigerant discharged from a compressor toevaporators disposed in a plurality of showcases, comprises chamberinside temperature sensors which detect chamber inside temperatures ofthe showcases, respectively, and control means for controlling anoperation of the compressor, and this control means controls theoperation of the compressor on the basis of the chamber insidetemperature of the showcase that is hardest to cool among the respectiveshowcases. Therefore, as compared with a case where the operation iscontrolled in accordance with a low pressure, the control is hard to beaffected by an operation of an opening/closing valve, an expansion valveor the like of each showcase.

In consequence, a fluctuation of an operation state of the compressor isinhibited, and a power consumption is decreased. On the other hand, thecooling of the showcase that is hardest to cool among the respectiveshowcases is securely performed, and hence, an energy loss due to anexcessive ability of the compressor to the other showcases is alsoeliminated. Consequently, according to the present invention, all of theplurality of showcases can be cooled with no difficulty, whilesuppressing the power consumption in the compressor.

In this case, as in the invention of claim 2, when each of the showcasescomprises superheat degree regulating means for throttling therefrigerant flowing into the evaporator and regulating, into apredetermined value, the superheat degree of the refrigerant flowing outfrom the evaporator, and an opening/closing valve which controls theinflow of the refrigerant into the evaporator, i.e., when a so-calledmechanical expansion valve is employed as the superheat degreeregulating means, the control means controls the operation of thecompressor on the basis of the chamber inside temperature of theshowcase that is hardest to cool, sets a target superheat degree of theother showcase on the basis of the chamber inside temperatures of theother showcases, and opens and closes the opening/closing valve on thebasis of this target superheat degree and the predetermined value of thesuperheat degree. In consequence, it is possible to smoothly executechamber inside temperature control of all the showcases by the controlof the compressor in accordance with the showcase that is hardest tocool and by the control of the opening/closing valves of the othershowcases.

In addition, as in the invention of claim 3, when each of the showcasescomprises superheat degree regulating means for throttling therefrigerant flowing into the evaporator and regulating, into apredetermined value, the superheat degree of the refrigerant flowing outfrom the evaporator, and an opening/closing valve which controls theinflow of the refrigerant into the evaporator, i.e., when the so-calledmechanical expansion valve is employed as the superheat degreeregulating means, the control means controls the operation of thecompressor on the basis of the chamber inside temperature of theshowcase that is hardest to cool, opens and closes the opening/closingvalve of the other showcases on the basis of the chamber insidetemperatures of the other showcases, and executes the opening andclosing of the respective opening/closing valves at different timings,when the opening/closing valves of the other showcases are opened andclosed. In consequence, while smoothing executing the chamber insidetemperature control of all the showcases by the control of thecompressor in accordance with the showcase that is hardest to cool andthe control of the opening/closing valves of the other showcases, adisadvantage that the opening/closing valves of the plurality ofshowcases are synchronously opened and closed is eliminated, and afluctuation of an operation state of the compressor is accordinglyinhibited.

In addition, as in the invention of claim 4, when each of the showcasescomprises an expansion valve which throttles the refrigerant flowinginto the evaporator and controls, into a target superheat degree, thesuperheat degree of the refrigerant flowing out from the evaporator,i.e., when a so-called electronic expansion valve is employed as theexpansion valve, the control means defines, as a predetermined value,the target superheat degree of the showcase that is hardest to cool tocontrol a valve open degree of an expansion valve of the showcase,controls the operation of the compressor on the basis of the chamberinside temperature of the showcase, sets the target superheat degree ofthe other showcases on the basis of the chamber inside temperatures ofthe other showcases, and controls the valve open degree of the expansionvalve of the other showcases. In consequence, it is possible to smoothlyexecute the chamber inside temperature control of all the showcases bythe control of the compressor in accordance with the showcase that ishardest to cool and by the control of the opening/closing valves of theother showcases.

Furthermore, as in the invention of claim 5, the control meansdistinguishes the showcase that is hardest to cool among the respectiveshowcases, and in a case where there is present the other showcase thatis harder to cool than the showcase in which the operation of thecompressor is controlled on the basis of the chamber inside temperature,the control means switches to a state to control the operation of thecompressor on the basis of the chamber inside temperature of the othershowcases. In consequence, even when the showcase that is hardest tocool is replaced due to a change of a load of each showcase, or thelike, it is possible to switch the operation state with no difficulty.

In this case, as in the invention of claim 6, the control meansdistinguishes the showcase that is hardest to cool among the respectiveshowcases, in a state where the chamber inside temperature isstabilized, so that it is possible to effectively prevent occurrence ofwrong judgment due to the distinguishing during defrosting or duringpull-down.

Further, when the control means controls an operation frequency of thecompressor on the basis of the chamber inside temperature of theshowcase that is hardest to cool as in the invention of claim 7, theabove invention is especially effective.

Furthermore, as in the invention of claim 8, when the showcase coolingdevice comprises a blowout temperature sensor disposed in a cold airblowout portion of each of the showcases to detect a blowout temperatureof the cold air to each of the showcases, the control means determines atarget blowout temperature of the cold air to the showcase by a PIDcalculation based on a deviation between the chamber inside temperatureof the showcase and a set value of the chamber inside temperature, anddetermines a target operation frequency of the compressor and/or thetarget superheat degree by a PID calculation based on a deviationbetween the blowout temperature detected by the blowout temperaturesensor and the target blowout temperature. In this case, the chamberinside temperature which moderately changes and the blowout temperaturewhich steeply changes are classified to perform the respective PIDcalculations, the compressor and the opening/closing valve or theexpansion valve can be controlled, and it is possible to exactly realizecooling control by eliminating a time lag of the refrigerant supply tothe evaporator of each showcase as much as possible.

Additionally, as in the invention of claim 9, when the showcase coolingdevice comprises evaporator temperature sensors to detect temperaturesof the evaporators of the showcases, respectively, the control meansdetermines a target evaporator temperature of each of the showcases by aPID calculation based on a deviation between the chamber insidetemperature of the showcase and a set value of the chamber insidetemperature, and determines a target operation frequency of thecompressor and/or the target superheat degree by a PID calculation basedon a deviation between the temperature of each of the evaporators whichis detected by the evaporator sensor and the target evaporatortemperature. Also in this case, the chamber inside temperature whichmoderately changes and the temperature of the evaporator which steeplychanges are classified to perform the respective PID calculations, thecompressor and the opening/closing valve or the expansion valve can becontrolled, and it is possible to exactly realize cooling control byeliminating a time lag of the refrigerant supply to the evaporator ofeach showcase as much as possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pipe constitutional view of a showcase cooling device of anembodiment to which the present invention is applied;

FIG. 2 is a pipe constitutional view in a refrigerating machine of theshowcase cooling device of FIG. 1;

FIG. 3 is a pipe constitutional view in a showcase of the showcasecooling device of FIG. 1 (Embodiment 1);

FIG. 4 is a control constitutional view of the showcase cooling deviceof FIG. 1;

FIG. 5 is a view showing data communication of the showcase coolingdevice of FIG. 4;

FIG. 6 is a timing chart explaining another liquid solenoid valvecontrol by a main control device of FIG. 4 in the case of the showcaseof FIG. 3 (Embodiment 2);

FIG. 7 is another pipe constitutional view in the showcase of theshowcase cooling device of FIG. 1 (Embodiment 3);

FIG. 8 is a control constitutional view of the showcase cooling deviceof FIG. 7; and

FIG. 9 is a control block diagram of a compressor operation frequency, aliquid solenoid valve, and an electronic expansion valve by a maincontrol device of each of FIG. 4 and FIG. 8.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

Embodiment 1

In a pipe constitutional view of FIG. 1, a showcase cooling device 1 ofan embodiment cools a plurality of showcases 3A to 3H installed in astore interior 2 of a convenience store (a store). In an exterior of thestore, a refrigerating machine 6 connected to the respective showcases3A to 3H via refrigerant pipes 4 and 5, and the showcases 3A to 3H andthe refrigerating machine 6 constitute the showcase cooling device 1 ofthe embodiment.

It is to be noted that the showcases 3A to 3F are open showcases, and inthe showcases 3A and 3C to 3F among these showcases, chilled foods(commodities) are displayed and sold chamber insides (the displaychambers), and insides of the chambers are cooled in a comparatively lowrefrigeration temperature zone (0° C. to +5° C.) which is suitable forthe cooling of the chilled foods. In the showcase 3B, boxed lunches (thecommodities) are displayed and sold in a chamber (the display chamber),and the inside of the chamber is cooled in a refrigeration temperaturezone of comparatively high temperatures (+15° C. to +20° C.) which issuitable for the cooling of the boxed lunches. In addition, although notshown in the drawing, a refrigeration showcase is also installed todisplay frozen foods or ice creams in a refrigerating state (−20° C. to−25° C.)

On the other hand, the showcases 3G and 3H are closed type showcasesreferred to as walk-in showcases comprising transparent glass doors andinstalled on a wall surface of the store, beverages or the like (thecommodities) are displayed and sold chamber insides (display chambers),and an inside of each chamber is cooled in a refrigeration temperaturezone (0° C. to +5° C.) which is suitable for the cooling of thebeverages. Further, the respective showcases 3A to 3H are connected inparallel to the refrigerating machine 6 by the refrigerant pipes 4 and5.

FIG. 2 shows a pipe constitution in the refrigerating machine 6 ofFIG. 1. In the refrigerating machine 6, there are disposed a compressor7 to be driven by a motor 7M, a condenser 8, a blower 9 for thecondenser, various sensors including a low pressure sensor 11, and thelike. Further, a discharge pipe 7D (a high pressure side) of thecompressor 7 is connected to an inlet pipe 8A of the condenser 8, and anoutlet pipe 8B of the condenser 8 is connected to the refrigerant pipe 4toward the store interior 2. In addition, a suction pipe 7S (a lowpressure side) of the compressor 7 is connected to the refrigerant pipe5 from the store interior 2. Further, the blower 9 for the condenser isoperated to air-cool the condenser 8. In addition, the low pressuresensor 11 is disposed to detect a refrigerant pressure of the suctionpipe 7S of the compressor 7.

On the other hand, FIG. 3 shows a pipe constitution in each of theshowcases 3A to 3H of FIG. 1. In each of the showcases 3A to 3H of thisembodiment, there are disposed a liquid solenoid valve 12 as anopening/closing valve, a mechanical expansion valve 13 as superheatdegree regulating means, an evaporator 14, a blower 16 for cold aircirculation, respective main sensors including an chamber insidetemperature sensor 17, a blowout temperature sensor 18, and a suctiontemperature sensor 19, and the like. Further, an outlet of the liquidsolenoid valve 12 is connected to the expansion valve 13, an outlet ofthe expansion valve 13 is connected to the evaporator 14, an inlet pipe12A of the liquid solenoid valve 12 is connected to the refrigerant pipe4, and an outlet pipe 14A of the evaporator 14 is connected to therefrigerant pipe 5. As described above, series circuits of the liquidsolenoid valves 12, the expansion valves 13 and the evaporators 14 inthe respective showcases 3A to 3H are connected in parallel between therefrigerant pipes 4 and 5.

The blower 16 for cold air circulation sucks cold air of a chamberinside 21, thereby allowing the evaporator 14 to perform heat exchangebetween the cold air and the evaporator, and the blower blows the coldair outwardly to the chamber inside 21, thereby cooling the chamberinside 21 in the abovementioned refrigeration temperature zone. Inaddition, the chamber inside temperature sensor 17 is disposed to detecta temperature (an chamber inside temperature) of the chamber inside 21,the blowout temperature sensor 18 is disposed to detect a temperature (ablowout temperature) of the cold air to be blown out to the chamberinside 21, and the suction temperature sensor 19 is disposed to detect atemperature (a suction temperature) of the cold air to be sucked fromthe chamber inside 21 to the blower 16 for cold air circulation.

According to such a pipe constitution, the compressor 7 and thecondenser 8 of the refrigerating machine 6 and the expansion valves 13and the evaporators 14 of the showcases 3A to 3H constitute a well-knownrefrigerant circuit 22. An operation frequency of the motor 7M of thecompressor 7 of the refrigerating machine 6 of the embodiment iscontrolled. When the compressor 7 is operated, a gas refrigerantcompressed to have a high temperature and high pressure flows into thecondenser 8 in which the refrigerant is then air-cooled by the blower 9for the condenser to condense. The refrigerant (a liquid refrigerant)allowed to condense in the condenser 8 reaches the store interior 2through the refrigerant pipe 4, and is distributed and supplied from thestore interior to each of the showcases 3A to 3H.

The liquid refrigerant flowing into each of the showcases 3A to 3Hreaches the expansion valve 13 through the liquid solenoid valve 12, isthrottled and decompressed in the expansion valve, and flows into theevaporator 14. The refrigerant flowing into the evaporator 14evaporates, and exerts a cooling effect by a heat absorbing operationgenerated at this time. Further, the refrigerant flowing out from theevaporator 14 returns to the refrigerating machine 6 through therefrigerant pipe 5, and is sucked by the compressor 7, thereby repeatingthis circulation.

The mechanical expansion valve 13 of this embodiment self-sustainablycontrols a throttle degree of the expansion valve by an operation ofbellows (not shown) which expand and contract in accordance with atemperature of the outlet pipe 14A of the evaporator 14, and a superheatdegree of the refrigerant flowing out from the evaporator 14 isregulated into a predetermined value set in advance (e.g., a fixedsuperheat degree of 3K). In consequence, the refrigerant supply to theevaporator 14 is regulated, and liquid back to the compressor 7 isprevented.

Next, FIG. 4 and FIG. 5 show a control constitution of the showcasecooling device 1. In each drawing, 23 is a main control device referredto as a store master. This main control device 23 is installed in amanagement room of the store, or the like to centrally controloperations of the refrigerating machine 6 and the respective showcases3A to 3H. Also in the refrigerating machine 6 and the respectiveshowcases 3A to 3H, a refrigerating machine control device 24 andshowcase control devices 26 are disposed, respectively, and connected tothe main control device 23 by a communication line 27. Each of the maincontrol device 23, the refrigerating machine control device 24 and theshowcase control devices 26 is constituted of a microcomputer, and thesemicrocomputers constitute control means of the showcase cooling device1.

Separate ID numbers of, e.g., 101 to 108 are given to the respectiveshowcase control devices 26, and an ID number of 301 is given to therefrigerating machine control device 24. The main control device 23identifies the respective showcase control devices 26 and therefrigerating machine control device 24 by these ID numbers, andreceives, from each of the showcase control devices 26, data or the likeconcerning the chamber inside temperature, the blowout temperature andthe suction temperature of each of the showcases 3A to 3H as shown inFIG. 5. Further, the main control device 23 transmits data or the likeconcerning an opening/closing instruction of the liquid solenoid valve12 to the showcase control device 26 of each of the showcases 3A to 3H,and transmits data or the like concerning a target value instruction ofa target low pressure or a target operation frequency or the like of thecompressor 7 to the refrigerating machine control device 24 of therefrigerating machine 6.

In addition, the main control device 23 is connected to atemperature/humidity sensor 28. The temperature/humidity sensor 28detects a temperature/humidity of the store interior 2. The main controldevice 23 calculates an enthalpy of the store interior 2 on the basis oftemperature/humidity data of the store interior 2 which is detected bythe temperature/humidity sensor 28, and sets the target low pressure ofthe refrigerant circuit 22. It is to be noted that this target lowpressure is set to such a value that all the showcases 3A to 3H cansufficiently be cooled. Additionally, in the main control device 23, aset value of the chamber inside temperature of each of the showcases 3Ato 3H can be input, and data such as the chamber inside temperature ofeach of the showcases 3A to 3H can be confirmed, thereby realizingcentral management of the showcases 3A to 3H in the store by use of themain control device 23.

Next, an operation of the showcase cooling device 1 of this embodimenthaving the above constitution will be described. First, the main controldevice 23 always monitors the chamber inside temperature (detected bythe chamber inside temperature sensor 17) received from each of theshowcase control devices 26, and compares the temperature with the setvalue of the chamber inside temperature of each of the showcases 3A to3H, to monitor cooling degrees of these showcases. Further, among therespective showcases 3A to 3H, the showcase that is hardest to cool isdistinguished. For example, in a case where, as compared with the othershowcases, the liquid solenoid valve 12 of each of the showcases 3G and3H continues to be opened but a long time is required until the chamberinside temperature reaches the set value or a state that the chamberinside temperature is the set value or more lasts long, or the like, themain control device 23 determines each of the showcases 3G and 3H as theshowcase that is hardest to cool. It is to be noted that the number ofthe showcases is not limited to two in this manner, and the number ofthe showcases is one in a certain case.

When each of the showcases 3G and 3H is determined as the showcase thatis hardest to cool in this manner, the main control device 23 transmitsan instruction to the showcase control device 26 of each of theshowcases 3G and 3H to set the liquid solenoid valve 12 to a 100% openstate. In consequence, the liquid refrigerant throttled by the expansionvalve 13 is always supplied to the evaporator 14 of each of theshowcases 3G and 3H (an operation ratio of 100%). In addition, the maincontrol device 23 controls the operation frequency of the compressor 7(the motor 7M) of the refrigerating machine 6 on the basis of thechamber inside temperature of each of the showcases 3G and 3H, andcontrols the chamber inside temperature of each of the showcases 3G and3H into the set value.

A specific control system in this case will be described with referenceto FIG. 9. First, the main control device 23 compares the chamber insidetemperature detected by the chamber inside temperature sensor 17 of eachof the showcases 3G and 3H with the set value (a target value), and aPID calculating section 31 performs a PID calculation of a deviation e1between the temperature to determine a target blowout temperature (acontrol amount). Next, the main control device compares the blowouttemperature detected by the blowout temperature sensor 18 of each of theshowcases 3G and 3H with the target blowout temperature, and a PIDcalculating section 32 performs a PID calculation of a deviation e2between the temperatures to determine the target operation frequency (acontrol amount) of the compressor 7.

The determined target operation frequency is instructed from the maincontrol device 23 to the refrigerating machine control device 24 of therefrigerating machine 6. The refrigerating machine control device 24controls the operation frequency of the compressor 7 (the motor 7M) tomatch the received target operation frequency. Here, when the coolingeffect in the evaporator 14 varies due to the change of the operationfrequency of the compressor 7, the chamber inside temperature of each ofthe showcases 3G and 3H moderately changes, but the blowout temperaturesteeply changes. Therefore, as in the embodiment, when the chamberinside temperature which moderately changes and the blowout temperaturewhich steeply changes are classified to perform the PID calculations bythe PID calculating sections 31 and 32, respectively, a time lag of therefrigerant supply from the compressor 7 to the evaporator of each ofthe showcases 3G and 3H decreases.

On the other hand, as to the other showcases 3A to 3F that more easilycool than the showcases 3G and 3H, the main control device 23 determinesthe target superheat degree on the basis of the chamber insidetemperature detected by the chamber inside temperature sensor 17 of eachof the showcases 3A to 3F and the set value. Also in the determinationof this target superheat degree, the main control device 23 similarlyperforms the PID calculation of FIG. 9. However, an operation amount ofthe PID calculating section 32 in this case is the target superheatdegree of the showcases 3A to 3F. That is, when the chamber insidetemperature is higher than the set value, the target superheat degreebecomes smaller, and when the chamber inside temperature is lower, thetarget superheat degree becomes larger.

The main control device 23 calculates an opening/closing ratio of theliquid solenoid valve 12 of each of the showcases 3A to 3F on the basisof the determined target superheat degree and the predetermined value(the fixed superheat degree of 3K) of the superheat degree of theexpansion valve 13. For example, when the target superheat degree of theshowcase 3D is 5K, the opening/closing ratio (i.e., the operation ratio)of the liquid solenoid valve 12 is 60%. The main control device 23transmits the instruction concerning the opening and closing of theliquid solenoid valve 12 to each of the showcase control devices 26 onthe basis of the determined opening/closing ratio concerning each of theshowcases 3A to 3F. The showcase control device 26 opens and closes(turns on and off) the liquid solenoid valve 12 on the basis of thereceived opening/closing instruction, thereby controlling the chamberinside temperature of each of the showcases 3A to 3F into the set value.

Thus, the main control device 23 controls the operation of thecompressor 7 on the basis of the chamber inside temperature of theshowcase that is hardest to cool among the respective showcases 3A to3H, and hence, the compressor is hard to be influenced by the operationof the liquid solenoid valve 12 of each of the showcases 3A to 3H ascompared with the operation of the compressor is controlled inaccordance with the low pressure. In consequence, a fluctuation of anoperation state of the compressor 7 is inhibited, and a powerconsumption is reduced. On the other hand, the cooling of the showcasethat is hardest to cool (each of 3G and 3H in the embodiment) among therespective showcases 3A to 3H is securely performed, and hence, anenergy loss due to an excessive ability of the compressor 7 to the othershowcases (3A to 3F in the embodiment) is also eliminated. Consequently,all of the plurality of showcases 3A to 3H can be cooled with nodifficulty, while suppressing the power consumption in the compressor 7.

In particular, when the mechanical expansion valve is employed as theexpansion valve 13 as in this embodiment, the main control device 23controls the operation of the compressor 7 on the basis of the chamberinside temperature of the showcase that is hardest to cool (each of 3Gand 3H in the embodiment), sets the target superheat degree of theshowcase on the basis of the chamber inside temperatures of the othershowcases (3A to 3F in the embodiment), and calculates theopening/closing ratio of the liquid solenoid valve 12 on the basis ofthis target superheat degree and the predetermined value (the fixedsuperheat degree) to open and close the valve, so that it is possible tosmoothly execute chamber inside temperature control of all the showcases3A to 3H by the control of the compressor 7 in accordance with theshowcase that is hardest to cool and by the control of the liquidsolenoid valves 12 of the other showcases. In consequence, there is alsothe effect that the abovementioned setting control of the target lowpressure on the basis of the store interior enthalpy by thetemperature/humidity sensor 28 is not required.

It is to be noted that, as described above, the main control device 23always monitors a cooling state of each of the showcases 3A to 3H, anddistinguishes the showcase that is hardest to cool among the showcases.Further, in a case where there is present the other showcase that isharder to cool than the showcases 3G and 3H in which the operationfrequency of the compressor 7 is controlled on the basis of the chamberinside temperatures at present, the control means determines the othershowcase as the showcase that is hardest to cool, and switches to such astate to control the operation of the compressor 7 on the basis of thechamber inside temperature of the showcase. In consequence, even whenthe showcase that is hardest to cool is replaced due to a change of anamount of the commodities on display (loads) of each of the showcases 3Ato 3H, a change of environment, or the like, it is possible to switchthe operation state with no difficulty.

However, the main control device 23 executes the distinguishing of theshowcase that is hardest to cool as described above only when thechamber inside temperature of each of the showcases 3A to 3H isstabilized. That is, such distinguishing of the showcase that is hardestto cool is not performed during defrosting (to be executed four times aday) of each of the showcases 3A to 3H or during pull-down, but acontrol state prior to the defrosting is maintained. In consequence,occurrence of wrong judgment is avoided.

Embodiment 2

Here, in the above embodiment, as to the other showcases 3A to 3F, thetarget superheat degree is determined to calculate the opening/closingratio of the liquid solenoid valve 12, thereby controlling the chamberinside cooling of these showcases, but the present invention is notlimited to this embodiment, and the opening and closing of each liquidsolenoid valve 12 may be controlled on the basis of an chamber insidetemperature of each of the showcases 3A to 3F and a set value of thechamber inside temperature. In this case, the liquid solenoid valve 12is opened/closed on the basis of an ON-temperature (an upper limitvalue) and an OFF-temperature (a lower limit value) that are set aboveand below the set value of the chamber inside temperature by use ofpredetermined differentials (the set value becomes an averagetemperature). However, when the values are used as they are and loads ofthe respective showcases 3A to 3F are similar, the liquid solenoidvalves 12 disadvantageously synchronously open and close, and there isthe risk that, due to an influence of the valves, an operation frequencyof a compressor 7 noticeably fluctuates.

To solve the problem, FIG. 6 shows a control example by a main controldevice 23 to eliminate such a disadvantage. A top stage of FIG. 6 showsa case that the liquid solenoid valve 12 is opened at the ON-temperatureand closed at the OFF-temperature as described above. When therespective showcases 3A to 3F have the same ease of cooling, thereenlarges the risk that the liquid solenoid valves 12 of all theshowcases 3A to 3F synchronously open and close. Therefore, controlprocesses of a second stage from the top, a third stage from the top anda bottom stage including the top stage of FIG. 6 are combined andexecuted in the showcases 3A to 3F, respectively. That is, for example,the showcase 3A is controlled as shown in the top stage, the showcases3C and 3D are controlled as shown in the second stage from the top, theshowcase 3F is controlled as shown in the third stage from the top, andthe showcase 3B is controlled as shown in the bottom stage.

The control of the second stage from the top of FIG. 6 is control toopen the liquid solenoid valve 12 when the chamber inside temperature isthe ON-temperature or more and to close the valve when the chamberinside temperature is lower than the set value. In this case, ascompared with the case of the top stage, the liquid solenoid valve 12 ismore frequently opened and closed, and the average temperature (a boldbroken line) is slightly higher than the set value. In addition, thecontrol of the third stage from the top of FIG. 6 is control to open theliquid solenoid valve 12 when the chamber inside temperature is theON-temperature or more and to close the valve when the chamber insidetemperature is lower than the ON-temperature. In this case, the liquidsolenoid valve 12 is further frequently opened and closed, and theaverage temperature (a bold broken line) is further higher than the setvalue. In addition, the control of the bottom stage of FIG. 6 is controlto open the liquid solenoid valve 12 when the chamber inside temperatureis the ON-temperature or more and to close the valve when thetemperature turns to drop. In this case, the liquid solenoid valve 12 isfurther frequently opened and closed, and the average temperature (abold broken line) is further higher than the set value. Therefore, theset value is beforehand shifted to be lower as much as the averagetemperature heightens.

In this case, the control of the upper stage of FIG. 6 may be assignedto the showcase that is harder to cool and harder to warm (a temperaturechange is larger), and the control of the lower stage of FIG. 6 may beassigned to the showcase that is easier to cool and easier to warm (thetemperature change is smaller). The showcases that are hard to cool(hard to warm) or easy to cool (easy to warm) are ranked in accordancewith the change of the chamber inside temperature after theopening/closing of the liquid solenoid valve 12 in a state where thechamber inside temperature is stabilized of a fluctuation width of thetemperature.

Thus, the opening/closing control processes of the liquid solenoidvalves 12 are combined and executed in the respective showcases 3A to3F, and hence, operation timings of the respective liquid solenoidvalves 12 shift from one another and opening/closing operations of thevalves are performed at different timings. In consequence, whilesmoothly executing the chamber inside temperature control of all theshowcases 3A to 3H by the operation control of the compressor 7 inaccordance with the showcases 3G and 3H that are hardest to cool and bythe control of the liquid solenoid valve 12 of each of the othershowcases 3A to 3F, there is eliminated the disadvantage that theopening/closing valves of the plurality of showcases 3A to 3F aresynchronously opened and closed, and a fluctuation of an operation stateof the compressor 7 due to the disadvantage is also inhibited.

It is to be noted that, in the above embodiment, a temperature to openand close the liquid solenoid valve 12 is switched to shift theopening/closing timing, but the present invention is not limited to theembodiment, and the differentials of the ON-temperature and theOFF-temperature are used as they are, and the set value may be shiftedto a different value for each of the showcases 3A to 3F.

Embodiment 3

Next, there will be described control in a case where, for example, anelectronic expansion valve (an electric expansion valve) operated by astepping motor is used as an expansion valve of each of the showcases 3Ato 3H. FIG. 7 is a pipe constitutional view in each of the showcases 3Ato 3H in this case, and FIG. 8 is a control constitutional view. It isto be noted that, in the respective drawings, parts denoted with thesame symbols as in FIG. 3 to FIG. 5 produce the same or similarfunctions.

In this case, an electronic expansion valve (an electric expansionvalve) 33 is employed in place of a mechanical expansion valve in eachof the showcases 3A to 3H. In addition, an evaporator inlet temperaturesensor 36 and an evaporator outlet temperature sensor 37 are disposed inan inlet pipe 14B and an outlet pipe 14A of an evaporator, respectively,and the sensors detect a temperature of a refrigerant flowing into anevaporator 14 and a temperature of the refrigerant flowing out from theevaporator 14. Further, outputs of the sensors are transmitted to a maincontrol device 23 via a showcase control device 26, and the main controldevice 23 calculates a superheat degree of the evaporator 14 from adifference between the temperatures. In addition, a valve open degree ofthe expansion valve 33 is controlled by the main control device 23 viathe showcase control device 26.

Next, an operation in this case will be described. Also in this case,the main control device 23 always monitors an chamber inside temperature(detected by an chamber inside temperature sensor 17) received from eachof the showcase control devices 26, compares the chamber insidetemperature with a set value of the chamber inside temperature of eachof the showcases 3A to 3H, and monitors cooling degrees of theshowcases. Further, among the respective showcases 3A to 3H, theshowcase that is hardest to cool is distinguished. For example, in acase where, as compared with the other showcases, the valve open degreeof the expansion valve 33 of each of the showcases 3G and 3H continuesto be large but a long time is required until the chamber insidetemperature reaches the set value or a state that the chamber insidetemperature is the set value or more lasts long, or the like, the maincontrol device 23 determines each of the showcases 3G and 3H as theshowcase that is hardest to cool. It is to be noted that the number ofthe showcases is not limited to two in this manner, and the number ofthe showcases is one in a certain case.

When each of the showcases 3G and 3H is determined as the showcase thatis hardest to cool in this manner, the main control device 23 transmitsan instruction to the showcase control device 26 of each of theshowcases 3G and 3H to control the valve open degree of the expansionvalve 33 so that a superheat degree of the evaporator 14 becomes apredetermined value (e.g., 5K). In addition, the main control device 23controls an operation frequency of a compressor 7 (a motor 7M) of arefrigerating machine 6 on the basis of the chamber inside temperatureof each of the showcases 3G and 3H. A specific control system in thiscase is similar to FIG. 9. In consequence, the chamber insidetemperature of each of the showcases 3G and 3H is controlled into theset value.

On the other hand, as to the other showcases 3A to 3F that are easier tocool than the showcases 3G and 3H, the main control device 23 determinesa target superheat degree on the basis of the chamber inside temperatureof each of the showcases 3A to 3F which is detected by the chamberinside temperature sensor 17 and the set value. Also in thedetermination of this target superheat degree, the main control device23 similarly performs a PID calculation of FIG. 9. Additionally, anoperation amount of a PID calculating section 32 in this case is thetarget superheat degree of each of the showcases 3A to 3F. That is, whenthe chamber inside temperature is higher than the set value, the targetsuperheat degree becomes smaller, and when the temperature is lower, thedegree becomes larger.

The main control device 23 determines a target valve open degree of theexpansion valve 33 so that the superheat degree of the evaporator 14 ofeach of the showcases 13A to 13F becomes the determined target superheatdegree. The main control device 23 transmits, to each of the showcasecontrol devices 26, an instruction concerning the valve open degree ofthe expansion valve 33 on the basis of the determined target valve opendegree concerning each of the showcases 3A to 3F. The showcase controldevice 26 controls the valve open degree of the expansion valve 33 onthe basis of the received target valve open degree. It is to be notedthat the liquid solenoid valve 12 is set to an open state. Inconsequence, the chamber inside temperature of each of the showcases 3Ato 3F is controlled into the set value. Additionally, in the embodiment,a liquid solenoid valve 12 is disposed in a previous stage of theexpansion valve 33, but the expansion valve 33 which is the electronicexpansion valve can fully be closed, and hence, the liquid solenoidvalve 12 may be omitted depending on a control followability.Furthermore, when the plurality of fully closed expansion valves 33 areopened, the valves are controlled so that timings of the opening vary,and hence, a fluctuation of an operation state of the compressor 7 canbe inhibited in the same manner as described above.

In consequence, when the electronic expansion valves 33 are employed asexpansion valves in the showcases 3A to 3H as in this embodiment, themain control device 23 defines the target superheat degree of each ofshowcases 3G and 3H that are hardest to cool as a predetermined value tocontrol the valve open degrees of the expansion valves 33 of theshowcases 3G and 3H, controls the operation of the compressor 7 on thebasis of the chamber inside temperatures of the showcases 3G and 3H,sets the target superheat degree of each of the showcases 3A to 3F onthe basis of the chamber inside temperatures of the other showcases 3Ato 3F, and controls the valve open degrees of the expansion valves 33 ofthe showcases 3A to 3F, so that it is possible to smoothly execute thechamber inside temperature control of all the showcases 3A to 3H by thecontrol of the compressor 7 in accordance with the showcases 3G and 3Hthat are hardest to cool and by the control of the expansion valves 33of the other showcases 3A to 3F.

It is to be noted that, in the above embodiments, there has beendescribed the system where the main control device 23 transmits thecontrol instruction of each of the liquid solenoid valves 12 or theexpansion valves 33 to each of the showcases 3A to 3H to control thevalve, but the present invention is not limited to the embodiments.Specifically, the main control device 23 may determine the showcase thatis hardest to cool, give, to the determined showcase, the instructionthat the showcase is the showcase that is hardest to cool, control theoperation frequency of the compressor 7 on the basis of the chamberinside temperature of the showcase, and transmit the target superheatdegree to each showcase, and the actual control of the liquid solenoidvalve 12 or the expansion valve 33 in each showcase may be executed bythe showcase control device 26 of each showcase.

Additionally, in the embodiments, there have been described the casewhere the mechanical expansion valves 13 are used in all the showcases3A to 3H and the case where the electronic expansion valves 33 are usedtherein, but the present invention is also effective for a case wherethe valves are mixed. In this case, as to the showcase in which themechanical expansion valve 13 is used and which is hardest to cool, aninstruction to open the liquid solenoid valve 12 is transmitted to theshowcase control device 26 of the showcase, and as to the showcase inwhich the electronic expansion valve 33 is used and which is hardest tocool, an instruction to define the target superheat degree as thepredetermined value and control the valve open degree of the expansionvalve 33 is transmitted to the showcase control device of the showcase.In addition, the compressor 7 of the refrigerating machine 6 iscontrolled on the basis of the chamber inside temperatures of theseshowcases. Furthermore, as to the other showcase in which the mechanicalexpansion valve 13 is used and which is easy to cool, theopening/closing ratio of the liquid solenoid valve 12 is calculated bythe main control device 23, and as to the other showcase in which theelectronic expansion valve 33 is used and which is easy to cool, thetarget superheat degree is calculated by the main control device.Additionally, the main control device gives the instruction to each ofthe showcase control devices 26.

Furthermore, in the above embodiments, the target blowout temperature isdetermined by the PID calculation based on the deviation between thechamber inside temperature and the set value of the chamber insidetemperature, and the target operation frequency of the compressor 7 andthe target superheat degree of the refrigerant flowing out from theevaporator 14 are determined by the PID calculation based on thedeviation between the blowout temperature detected by the blowouttemperature sensor 18 and the target blowout temperature, but thetemperature of the evaporator 14 can be employed because the temperaturesteeply changes. Therefore, the present invention is not limited to thisblowout temperature, and a temperature sensor which detects thetemperature of the evaporator 14 may be disposed, a target evaporatortemperature may be determined in accordance with the chamber insidetemperature and the set value, and a PID calculation may be performed onthe basis of the temperature of the evaporator 14 which is detected bythe temperature sensor of the evaporator 14 and the target evaporatortemperature, to determine the target operation frequency or the targetsuperheat degree.

Furthermore, in the embodiment, both of the target operation frequencyof the compressor 7 and the target superheat degree of the refrigerantflowing out from the evaporator 14 are determined by the control of FIG.9, but the present invention is not limited to the embodiment, and oneof the target superheat degree and the target operation frequency may bedetermined by the control of FIG. 9, and the other may be determined bya usual PID calculation based on the chamber inside temperature and theset value.

Additionally, in the embodiment, the present invention is applied to therefrigerant circuit in which the mechanical expansion valves or theelectronic expansion valves are used, but the invention of claim 1 isnot limited to the embodiment, and the invention is also effective for acase where the refrigerant flowing into the evaporator is throttled by acapillary tube.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 showcase cooling device    -   3A to 3H showcase    -   4 and 5 refrigerant pipe    -   6 refrigerating machine    -   7 compressor    -   8 condenser    -   12 liquid solenoid valve (opening/closing valve)    -   13 and 33 expansion valve    -   14 evaporator    -   17 chamber inside temperature sensor    -   17 blowout temperature sensor    -   23 main control device (control means)    -   24 refrigerating machine control device (control means)    -   26 showcase control device (control means)    -   31 and 32 PID calculating section

1. A showcase cooling device, which distributes and supplies arefrigerant discharged from a compressor to evaporators disposed in aplurality of showcases, comprising: chamber inside temperature sensorswhich detect chamber inside temperatures of the showcases, respectively;and control means for controlling an operation of the compressor,wherein the control means controls the operation of the compressor onthe basis of the chamber inside temperature of the showcase that ishardest to cool among the respective showcases.
 2. The showcase coolingdevice according to claim 1, wherein each of the showcases comprisessuperheat degree regulating means for throttling the refrigerant flowinginto the evaporator and regulating, into a predetermined value, thesuperheat degree of the refrigerant flowing out from the evaporator, andan opening/closing valve which controls the inflow of the refrigerantinto the evaporator, and the control means controls the operation of thecompressor on the basis of the chamber inside temperature of theshowcase that is hardest to cool, sets a target superheat degree of theother showcases on the basis of the chamber inside temperatures of theother showcases, and opens and closes the opening/closing valve of theother showcases on the basis of the target superheat degree and thepredetermined value of the superheat degree.
 3. The showcase coolingdevice according to claim 1, wherein each of the showcases comprisessuperheat degree regulating means for throttling the refrigerant flowinginto the evaporator and regulating, into a predetermined value, thesuperheat degree of the refrigerant flowing out from the evaporator, andan opening/closing valve which controls the inflow of the refrigerantinto the evaporator, and the control means controls the operation of thecompressor on the basis of the chamber inside temperature of theshowcase that is hardest to cool, opens and closes the opening/closingvalve of the other showcases on the basis of the chamber insidetemperatures of the other showcases, and executes the opening andclosing of the respective opening/closing valves at different timings,when the opening/closing valves of the other showcases are opened andclosed.
 4. The showcase cooling device according to claim 1, whereineach of the showcases comprises an expansion valve which throttles therefrigerant flowing into the evaporator and controls, into a targetsuperheat degree, the superheat degree of the refrigerant flowing outfrom the evaporator, and the control means defines, as a predeterminedvalue, the target superheat degree of the showcase that is hardest tocool to control a valve open degree of an expansion valve of theshowcase, controls the operation of the compressor on the basis of thechamber inside temperature of the showcase, sets the target superheatdegree of the other showcases on the basis of the chamber insidetemperatures of the other showcases, and controls the valve open degreeof the expansion valves of the other showcases.
 5. The showcase coolingdevice according to claim 1, wherein the control means distinguishes theshowcase that is hardest to cool among the respective showcases, and ina case where there is present the other showcase that is harder to coolthan the showcase in which the operation of the compressor is controlledon the basis of the chamber inside temperature, the control meansswitches to a state to control the operation of the compressor on thebasis of the chamber inside temperature of the other showcase.
 6. Theshowcase cooling device according to claim 5, wherein the control meansdistinguishes the showcase that is hardest to cool among the respectiveshowcases, in a state where the chamber inside temperature isstabilized.
 7. The showcase cooling device according to claim 1, whereinthe control means controls an operation frequency of the compressor onthe basis of the chamber inside temperature of the showcase that ishardest to cool.
 8. The showcase cooling device according to claim 7,which comprises a blowout temperature sensor disposed in a cold airblowout portion of each of the showcases to detect a blowout temperatureof the cold air to each of the showcases, wherein the control meansdetermines a target blowout temperature of the cold air to the showcaseby a PID calculation based on a deviation between the chamber insidetemperature of the showcase and a set value of the chamber insidetemperature, and determines a target operation frequency of thecompressor and/or the target superheat degree by a PID calculation basedon a deviation between the blowout temperature detected by the blowouttemperature sensor and the target blowout temperature.
 9. The showcasecooling device according to claim 7, which comprises evaporatortemperature sensors to detect temperatures of the evaporators of theshowcases, respectively, wherein the control means determines a targetevaporator temperature of each of the showcases by a PID calculationbased on a deviation between the chamber inside temperature of theshowcase and a set value of the chamber inside temperature, anddetermines a target operation frequency of the compressor and/or thetarget superheat degree by a PID calculation based on a deviationbetween the temperature of each of the evaporators which is detected bythe evaporator sensor and the target evaporator temperature.
 10. Theshowcase cooling device according to claim 2, wherein the control meansdistinguishes the showcase that is hardest to cool among the respectiveshowcases, and in a case where there is present the other showcase thatis harder to cool than the showcase in which the operation of thecompressor is controlled on the basis of the chamber inside temperature,the control means switches to a state to control the operation of thecompressor on the basis of the chamber inside temperature of the othershowcase.
 11. The showcase cooling device according to claim 10, whereinthe control means distinguishes the showcase that is hardest to coolamong the respective showcases, in a state where the chamber insidetemperature is stabilized.
 12. The showcase cooling device according toclaim 11, wherein the control means controls an operation frequency ofthe compressor on the basis of the chamber inside temperature of theshowcase that is hardest to cool.
 13. The showcase cooling deviceaccording to claim 12, which comprises a blowout temperature sensordisposed in a cold air blowout portion of each of the showcases todetect a blowout temperature of the cold air to each of the showcases,wherein the control means determines a target blowout temperature of thecold air to the showcase by a PID calculation based on a deviationbetween the chamber inside temperature of the showcase and a set valueof the chamber inside temperature, and determines a target operationfrequency of the compressor and/or the target superheat degree by a PIDcalculation based on a deviation between the blowout temperaturedetected by the blowout temperature sensor and the target blowouttemperature.
 14. The showcase cooling device according to claim 3,wherein the control means distinguishes the showcase that is hardest tocool among the respective showcases, and in a case where there ispresent the other showcase that is harder to cool than the showcase inwhich the operation of the compressor is controlled on the basis of thechamber inside temperature, the control means switches to a state tocontrol the operation of the compressor on the basis of the chamberinside temperature of the other showcase.
 15. The showcase coolingdevice according to claim 14, wherein the control means distinguishesthe showcase that is hardest to cool among the respective showcases, ina state where the chamber inside temperature is stabilized.
 16. Theshowcase cooling device according to claim 15, wherein the control meanscontrols an operation frequency of the compressor on the basis of thechamber inside temperature of the showcase that is hardest to cool. 17.The showcase cooling device according to claim 16, which comprises ablowout temperature sensor disposed in a cold air blowout portion ofeach of the showcases to detect a blowout temperature of the cold air toeach of the showcases, wherein the control means determines a targetblowout temperature of the cold air to the showcase by a PID calculationbased on a deviation between the chamber inside temperature of theshowcase and a set value of the chamber inside temperature, anddetermines a target operation frequency of the compressor and/or thetarget superheat degree by a PID calculation based on a deviationbetween the blowout temperature detected by the blowout temperaturesensor and the target blowout temperature.
 18. The showcase coolingdevice according to claim 4, wherein the control means distinguishes theshowcase that is hardest to cool among the respective showcases, and ina case where there is present the other showcase that is harder to coolthan the showcase in which the operation of the compressor is controlledon the basis of the chamber inside temperature, the control meansswitches to a state to control the operation of the compressor on thebasis of the chamber inside temperature of the other showcase.
 19. Theshowcase cooling device according to claim 18, wherein the control meansdistinguishes the showcase that is hardest to cool among the respectiveshowcases, in a state where the chamber inside temperature isstabilized.
 20. The showcase cooling device according to claim 19,wherein the control means controls an operation frequency of thecompressor on the basis of the chamber inside temperature of theshowcase that is hardest to cool.